You can get the kind of information you want on Tripadvisor. I don't know of any hotel in an area of downtown Montreal or Ottawa where there should be a concern for safety. The Residence Inn in downtown Montreal is very well located and has a nice breakfast. I never heard that having a room that's too big was a problem.
As for Ottawa, forget the Marriotts. If you like a small but very elegant room in a good location, choose the ARC. The Fairmount Chateau Laurier would be the most interesting place at the very high end. The Lord Elgin has a nice location and is a bit more reasonable.